We carried out ammonia nitrogen acute toxicity test by exposing Exopalaemon carinicauda larvae to chlorine ammonium in water. The half lethal concentration (LC₅₀) were 27.51, 23.15, 19.46 and 10.28 mg/L for larvae exposing 24, 48, 72 and 96 h to ammonia nitrogen, respectively. Accumulative toxicity in the body of E.carinicauda larvae was gradually increased with the exposing time. High concentrations of ammonia had an inhibitory effect on the molt of E.carinicauda larvae indicating a relationship dose-effect. In addition, the ammonia had a significant effect on nucleic acid metabolism and DNA synthesis in the spinal muscle cells. The value of RNA/DNA ratio in the spinal muscle cells was significant decline in the larvae exposed to high concentration of ammonia than those in control larvae. The metamorphosis rate of larvae exposing to ammonia showed a significant negative relation with the value of RNA/DNA ratio that indicated that the growth and metabolism of larvae was inhibited by ammonia nitrogen.